1. Field of the Invention
This invention relates to an improved ultrasonic range-determining device using a metal diaphragm in contact with a piezoelectric transducer.
2. Description of the Related Art
It is commonly known in the art that a piezoelectric crystal can be used as a transducer to emit a sonic or ultrasonic acoustic wave when excited by an AC voltage. Such a device may be used for determination of the distance of an object through the placement of a detector which senses when the emitted acoustic wave has reached the detector. Based on the time it takes the acoustic wave to reach the detector as well as the speed of the acoustic wave within the transmission medium, the distance from the source of the wave to the detector may be calculated. It is also known that the level of a liquid within a storage container may be determined through the use of a similar device and the concept of echo ranging. For example, U.S. Pat. No. 3,834,233 to Willis et al. discloses such a system. The system includes an ultrasonic transducer mounted at the top of a storage tank which directs an acoustic wave through the air down into a storage tank toward the surface of the liquid to be measured. Once the acoustic wave reaches the surface of the liquid, the wave's frequency is such that it will be reflected back toward the device which is equipped with a receiver to detect the reflected wave. The receiver thus detects the echo from the surface of the liquid and, based on the time for the signal to reach the surface of the liquid and return, calculates the distance from the ultrasonic transducer to the surface of the liquid.
However, such systems are not without their problems. Because such systems typically transmit the acoustic wave through a gaseous medium above the surface of the liquid to be measured, lower operating frequencies are required in order that the transmitted wave will be reflected at the liquid surface. These lower operating frequencies are less accurate in making distance measurements than higher frequencies. Such prior art systems have also been plagued by false signals received at the detector which did not originate from the device (such as outside noise) or which were not reflected from the material surface (i.e., reflected from the sides of the storage container). Prior art systems have also been plagued by the harsh conditions typically found within many industrial storage containers, particularly those storing corrosive substances. The quality of the device operation and the length of time these prior art detectors are able to maintain operation in such harsh environments result in their frequent malfunction and necessary replacement. Corrosive environments are especially hard on devices employing welded joints, epoxies or adhesives in their structures since it is at these points that corrosive effects are first manifested. Not only does the corrosive material itself decrease the operating life of such devices, but also changes in the operating environment of the device, including temperature and pressure changes, adversely affect such devices.
Finally, such prior art systems have been adversely affected by excessive dispersion of the emitted ultrasonic measurement beam such that the emitted signal is not strong enough to be reflected back to the device from a large distance (i.e. when the material in the storage container is at a low level). A weak emitted signal may also be caused by poor signal transfer within the device from the crystal to the emitting diaphragm. Another cause of poor device performance occurs when the detector radiates the transmitted signal in a number of directions, rather than in a narrow, focused beam, thereby increasing the possibility of falsely detecting reflected waves (e.g. from the storage container walls). The prior art has employed a variety of damping materials in various configurations to try and alleviate some of these problems. For example, U.S. Pat. No. 5,121,628, issued to Merkl et al. employs one such damping approach using lead pellets. For better signal transfer, the prior art has used bonding agents such as epoxies or solder, as disclosed in U.S. Pat. No. 4,000,650, issued to Snyder.
It is, therefore, an object of this invention to provide an ultrasonic transducer which detects the presence of an object or material and is resistant to malfunction or deterioration caused by changing temperature, changing pressure, corrosive environments, or a combination of these conditions.
It is another object of the present invention to provide an ultrasonic transducer which is installed within the fluid it is designed to measure.
It is still another object of the present invention to provide an ultrasonic transducer which has greater accuracy than that provided by existing devices.
It is yet another object of the present invention to provide an ultrasonic transducer with improved signal transfer, focus and strength resulting in a larger measurement range.
It is yet another object of the present invention to provide an ultrasonic transducer which is self-calibrating.
It is still another object of the present invention to provide an ultrasonic transducer having an improved, smaller size.
It is yet another object of the present invention to provide an ultrasonic transducer which can measure the material level of the contents within a storage container.
It is yet another object of the present invention to provide a reduced oil fill volume within the transducer for improved consistency of signal generation.
It is yet another object of the present invention to provide improved electrical lead connection within the transducer.
It is still another object of the present invention to provide a negative internal pressure within the transducer to improve diaphragm contact with the crystal.
It is another object of the present invention to provide an ultrasonic fluid-level detector which may be installed from the top, bottom, or side of the storage tank.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.